JP2008033376A - Imaging lens and imaging apparatus - Google Patents

Abstract

An imaging lens having a four-group, four-element configuration and an imaging apparatus using the imaging lens, which is small in size, can obtain higher imaging performance, is suitable for widening an angle, and has good image-side telecentric characteristics I will provide a.
In order from the object side, a positive lens, a negative lens, a positive lens, and a lens having at least one aspherical surface, and designed so as to satisfy a predetermined conditional expression, the size is reduced. An imaging lens having higher image forming performance and suitable image widening and having good image side telecentric characteristics is obtained.
[Selection] Figure 1

Description

  The present invention relates to an imaging lens of an imaging device using a solid-state imaging device such as a CCD (Charge Coupled Device) type image sensor or a CMOS (Complementary Metal-Oxide Semiconductor) type image sensor, and an imaging device using the imaging lens.

  Digital still cameras and digital video cameras equipped with an imaging device using a solid-state imaging device such as a CCD type image sensor or a CMOS type image sensor have been developed. Furthermore, since image pickup apparatuses using these solid-state image pickup elements are suitable for downsizing, in recent years, they have been mounted on small information terminals such as mobile phones. As the solid-state imaging device is further reduced in size and increased in pixel count, there is an increasing demand for downsizing and higher performance in imaging lenses mounted on these imaging apparatuses.

As an imaging lens for such an application, higher performance can be obtained as compared with a lens having two or three lenses. Therefore, in order from the object side, an aperture stop, a first lens having a positive refractive power, and a negative refraction. 2. Description of the Related Art A four-group four-lens lens is known that includes a second lens having power, a third lens having positive refractive power, and a fourth lens having positive or negative refractive power. Among these, a lens having a particularly short overall lens length (distance on the optical axis from the aperture stop to the image-side focal point) is disclosed in, for example, Patent Document 1.
JP 2002-365529 A

  Incidentally, the imaging lens of the type described in Patent Document 1 is a so-called telephoto type in which the first lens is a positive lens, the second lens is a negative lens, the third lens is a positive lens, and the fourth lens is a negative lens. This is a type that attempts to reduce the size of the imaging lens. However, on the other hand, the imaging lens of Patent Document 1 has a defect that aberration correction is insufficient to cope with the increase in the number of pixels of the solid-state imaging device or to widen the shooting angle of view.

  The present invention has been made in view of such problems, is small, can obtain higher imaging performance, is suitable for widening the angle, and has good image side telecentric characteristics. It is an object of the present invention to provide an imaging lens having a four-group four-lens configuration and an imaging apparatus using the imaging lens.

  The imaging lens according to the present invention includes, in order from the object side, a lens having positive refractive power (hereinafter, positive lens), a lens having negative refractive power (hereinafter, negative lens), a positive lens, and at least one surface having an aspherical shape. It is comprised from the lens which is. This configuration is a so-called triplet power arrangement. By designing the lens so as to satisfy a predetermined condition, spherical aberration, coma aberration, and chromatic aberration can be appropriately corrected in these lenses. Further, by disposing an aspherical fourth lens, it is possible to correct off-axis aberrations such as distortion and to obtain good image-side telecentric characteristics.

  Hereinafter, preferred embodiments of the present invention will be described.

The imaging lens according to Item 1, in order from the object side, a first lens that is a positive lens, a second lens that is a negative lens, a third lens that is a positive lens, and a fourth lens having at least one aspherical shape. It consists of a lens and satisfies the following conditional expression.
−3.0 <(r3 + r4) / (r3−r4) <− 0.7 (1)
ν1-ν2> 15.0 (2)
ν3-ν2> 15.0 (3)
r3: radius of curvature of the object side surface of the second lens r4: radius of curvature of the image side surface of the second lens ν1: Abbe number of the first lens ν2: Abbe number of the second lens ν3: Abbe number of the third lens The basic configuration of the present invention for obtaining a well-corrected imaging lens is, in order from the object side, a first lens that is a positive lens, a second lens that is a negative lens, a third lens that is a positive lens, and a fourth lens. It consists of a lens and satisfies the conditional expressions (1) to (3).

  The configuration of positive lens, negative lens, and positive lens in order from the object side is a so-called triplet type power arrangement, and spherical aberration, coma aberration, and chromatic aberration are appropriately corrected from the first lens to the third lens. can do. Furthermore, off-axis aberrations such as distortion can be corrected by the aspherical fourth lens, and good image-side telecentric characteristics can be obtained.

  Conditional expression (1) is a condition for appropriately setting the shape of the second lens. Within the range of the conditional expression, the second lens has a shape in which the object side surface has a strong negative refractive power. When the value shown in the conditional expression (1) is below the upper limit value of the expression, the negative refractive power on the side surface of the second lens object can be increased, and spherical aberration, coma aberration, field curvature, astigmatism, Effective for correcting chromatic aberration. On the other hand, the curvature of the image side surface of the second lens becomes gentle, and the aberration of the off-axis light beam passing near the periphery of this surface can be suppressed. In addition, since the principal point position of the second lens approaches the object side, the exit pupil position of the imaging lens can be located farther from the imaging plane, and thus good image side telecentric characteristics can be obtained. Can do. On the other hand, when the value shown in the conditional expression (1) exceeds the lower limit of the expression, the radius of curvature of the object side surface of the second lens does not become too small, and the lens does not have a problem in processing.

  Conditional expression (2) and conditional expression (3) are conditions for appropriately setting the Abbe numbers of the first lens to the third lens. By satisfying the conditions shown here, chromatic aberration generated in the first lens and the third lens having positive refractive power can be appropriately corrected by the second lens having negative refractive power.

  The imaging lens according to Item 2 is the configuration according to Item 1, wherein the imaging lens has an aperture stop closest to the object side. By having the aperture stop on the most object side, the distance from the imaging plane to the exit pupil position of the imaging lens can be increased, and good image-side telecentric characteristics can be obtained.

The imaging lens described in Item 3 satisfies the following conditional expression in the configuration described in Item 2.
-1.5 <(r3 + r4) / (r3-r4) <-0.7 (4)
r3: radius of curvature of object side surface of second lens r4: radius of curvature of image side surface of second lens Conditional expression (4) is a condition for appropriately setting the shape of the second lens. When the value shown in conditional expression (4) falls below the upper limit of the expression, the second lens has a meniscus shape or a plano-concave shape with the concave surface facing the object side, and corrects spherical aberration and chromatic aberration in the axial light beam. On the other hand, the occurrence of coma aberration can be suppressed in the off-axis light beam. Furthermore, it is preferable that the image side surface of the second lens and the object side surface of the third lens have a relatively close curvature and that both surfaces are arranged close to each other, so that on-axis and off-axis chromatic aberrations can be effectively corrected. In addition, since the principal point position of the second lens is closer to the object side, the exit pupil position of the imaging lens can be located farther from the imaging plane, and thus better image side telecentric characteristics can be obtained. Obtainable. In addition, since the negative power of the entire imaging lens is relatively disposed on the object side, it is easy to ensure a wide shooting angle of view and to ensure a sufficient back focus. On the other hand, when the value shown in the conditional expression (4) exceeds the lower limit of the expression, the radius of curvature of the object side surface of the second lens does not become too small, and accordingly, the curvature of the first lens image side surface becomes small. Therefore, it is possible to suppress deterioration of performance due to manufacturing errors on the side surface of the first lens image.

The imaging lens described in Item 4 satisfies the following conditional expression in the configuration described in Item 2 or 3.
-1.5 <(r3 + r4) / (r3-r4) <-1.0 (5)
r3: radius of curvature of the object side surface of the second lens r4: radius of curvature of the image side surface of the second lens Conditional expression (5) is a condition for more appropriately setting the shape of the second lens. When the value shown in the conditional expression (5) falls below the upper limit value of the expression, the second lens has a meniscus shape or a plano-concave shape with the concave surface facing the object side, and the axial light beam has more spherical aberration and chromatic aberration. It can be effectively corrected, and on the other hand, the occurrence of coma aberration can be more effectively suppressed in the off-axis light beam. Further, it is preferable that the image side surface of the second lens and the object side surface of the third lens have a relatively close curvature and that both surfaces are arranged close to each other, so that on-axis and off-axis chromatic aberration can be more effectively corrected. . In addition, since the principal point position of the second lens is closer to the object side, the exit pupil position of the imaging lens can be located farther from the imaging plane, and thus a better image side telecentric characteristic can be obtained. Obtainable. In addition, since the negative power in the entire imaging lens is relatively disposed on the object side, it is easier to ensure a wide shooting angle of view more effectively, and it is easier to ensure sufficient back focus. On the other hand, when the value shown in the conditional expression (5) exceeds the lower limit value of the expression, the radius of curvature of the object side surface of the second lens does not become too small. Therefore, it is possible to suppress the deterioration of the performance due to the manufacturing error of the image side surface of the first lens.

The imaging lens described in Item 5 satisfies the following conditional expression in the configuration described in any one of Items 2 to 4.
0.1 <(r1 + r2) / (r1-r2) <1.0 (6)
r1: radius of curvature of the object side surface of the first lens r2: radius of curvature of the image side surface of the first lens Conditional expression (6) is a condition for appropriately setting the shape of the first lens. In the range indicated by conditional expression (6), the image side surface of the first lens has a refractive power stronger than that of the object side surface. By satisfying the conditional expression (6), it is possible to suppress the occurrence of coma aberration on this surface without giving too much strong refractive power to the object side surface of the first lens. Further, the principal point position of the first lens approaches the image side. As a result, the exit pupil position of the photographic lens can be positioned farther from the imaging plane, and thus good image side telecentric characteristics can be obtained. Further, if the object side surface of the first lens closest to the aperture stop is aspherical, it is effective to correct the spherical aberration and coma aberration in the entire imaging lens in a balanced manner.

  The imaging lens according to Item 6 is the configuration according to any one of Items 2 to 5, wherein the fourth lens is a positive lens.

  When the fourth lens is a positive lens, the distance from the front principal point position of the imaging lens to the aperture stop increases. As a result, the exit pupil position of the photographic lens can be positioned farther from the imaging plane, and thus good image side telecentric characteristics can be obtained. Further, it is desirable because a back focus for installing a CCD cover glass, an infrared absorption filter, or an optical low-pass filter can be sufficiently secured.

  The imaging lens according to Item 7 is the configuration according to any one of Items 2 to 5, wherein the fourth lens is a negative lens.

  If the fourth lens is a negative lens, the overall length of the imaging lens can be kept short. At this time, it is desirable that the image side surface of the fourth lens be aspherical in order to maintain good image side telecentric characteristics at a high angle of view.

  The imaging lens according to item 8 is the configuration according to item 1, wherein the imaging lens has an aperture stop between the first lens and the second lens. By having an aperture stop between the first lens and the second lens, even when a member associated with the aperture stop, such as a light transmittance changing member such as a mechanical shutter or an ND filter, is mounted, Since it can be disposed between the first lens and the second lens, it is possible to shorten the entire length (length in the optical axis direction) of the entire imaging apparatus using the imaging lens.

  The imaging lens according to Item 9 is the configuration according to Item 8, wherein the first lens has a convex surface facing the object side.

  FIGS. 17 (a) and 17 (b) are cross-sectional views of an example in which the first lens attached to the light shielding member of the imaging device is shown together with the light shielding member. In FIG. 17 (a), the first lens is shown. L1 has a shape with a convex surface facing the object side. In FIG. 17B, the first lens L1 ′ has a shape with a concave surface facing the object side. Here, the first lens L1. Assuming that the distances from the portion closest to the image side of L1 ′ to the portion closest to the image side of the light shielding member C are respectively Δ and Δ ′, Δ <Δ ′, as is apparent in FIG. As shown in FIG. 17 (a), the first lens L1 has a convex surface facing the object side, so that a part of the first lens L1 enters the space in the stepped opening Ca of the light shielding member C. This is because space can be used effectively. By adopting such a configuration, it is possible to suppress the length in the optical axis direction of an imaging apparatus incorporating such an imaging lens and to realize a compact configuration.

The imaging lens described in Item 10 satisfies the following conditional expression in the configuration described in Item 8 or 9.
-1.5 <f2 / f <-0.7 (7)
f2: Focal length of the second lens f: Focal length of the entire image pickup lens system Conditional expression (7) is the focal point of the second lens under the conditions of the above-mentioned conditional expressions (1), (2), and (3). This is to optimize the distance. When the value of conditional expression (7) is less than the upper limit, the negative refractive power of the second lens does not become too strong, and good image side telecentric characteristics can be obtained. Moreover, by exceeding the lower limit, the negative refractive power of the second lens can be appropriately maintained, and the axial chromatic aberration can be favorably corrected.

  The imaging lens according to Item 11 is the configuration according to any one of Items 8 to 10, wherein the first lens and the second lens in the imaging lens are respectively on the aperture stop side with the aperture stop interposed therebetween. It has a meniscus shape with a concave surface. With such a configuration, it is easy to correct off-axis aberrations such as lateral chromatic aberration and distortion.

The imaging lens according to Item 12 satisfies the following conditional expression in the configuration according to any one of Items 8 to 11.
-2.5 <(r3 + r4) / (r3-r4) <-1.2 (8)
Conditional expression (8) is a condition for appropriately setting the shape of the second lens. When the value shown in conditional expression (8) is below the upper limit of the expression, the second lens has a meniscus shape with a concave surface facing the object side, and spherical aberration and chromatic aberration can be corrected in the axial light beam, On the other hand, the occurrence of coma aberration can be suppressed in the off-axis light beam. Furthermore, it is preferable that the image side surface of the second lens and the object side surface of the third lens have a relatively close curvature and that both surfaces are arranged close to each other, so that on-axis and off-axis chromatic aberrations can be effectively corrected. In addition, since the principal point position of the second lens is closer to the object side, the exit pupil position of the imaging lens can be located farther from the imaging plane, and thus better image side telecentric characteristics can be obtained. Obtainable. In addition, since the negative power of the entire imaging lens is relatively disposed on the object side, it is easy to ensure a wide shooting angle of view and to ensure a sufficient back focus. On the other hand, when the value shown in conditional expression (8) exceeds the lower limit value of the expression, the radius of curvature of the object side surface of the second lens does not become too small, and the chromatic aberration of magnification and distortion can be corrected more easily. can do. Since the first lens and the second lens are symmetrical with respect to the aperture stop, off-axis rays incident on the object side surface of the second lens are incident at an angle close to the normal of the surface. Therefore, even when the second lens has a strong meniscus shape as compared with an imaging lens having an aperture stop on the most object side, aberration correction can be performed satisfactorily.

  In the imaging lens according to Item 13, in the configuration according to any one of Items 8 to 12, the fourth lens is a negative lens.

  If the fourth lens is a negative lens, the overall length of the imaging lens can be kept short. At this time, it is desirable that the image side surface of the fourth lens be aspherical in order to maintain good image side telecentric characteristics at a high angle of view.

  The imaging lens according to item 14, wherein the air lens formed by the image side surface of the third lens and the object side surface of the fourth lens in the configuration according to any one of items 1 to 13, Biconcave shape. By forming the air lens between the third lens and the fourth lens into a biconcave shape, when the imaging lens is used in an imaging device due to its positive refractive power, the periphery of the imaging surface of the solid-state imaging device It is possible to easily secure the telecentric characteristics of the light beam that forms an image on the portion.

The imaging lens according to Item 15 satisfies the following conditional expression in the configuration according to any one of Items 1 to 14.
0.30 <fa / f <0.60 (9)
0.30 <r7 / f <2.0 (10)
f: focal length of the entire imaging lens system fa: focal length of the air lens formed by the image side surface of the third lens and the object side surface of the fourth lens, and a value fa = R6 · R7 calculated by the following equation /{R7.(1-N3)+R6.(N4-1)-D6.(1-N3).(N4-1)}
However,
N3: Refractive index with respect to d-line of third lens N4: Refractive index with respect to d-line of fourth lens R6: Radius of curvature of image side surface of third lens R7: Radius of curvature of object side surface of fourth lens D6: Third lens Air space r7 on the axis of the fourth lens: radius of curvature of the object side surface of the fourth lens Conditional expression (9) indicates that the air lens formed between the third lens image side surface and the fourth lens object side surface is positive. This is for appropriately setting the refractive power. By satisfying conditional expression (9), correction of field curvature and distortion and good image side telecentric characteristics can be ensured. Further, conditional expression (10) is for appropriately setting the refractive power of the object side surface of the fourth lens. By satisfying conditional expression (10), the refractive power of the air lens defined by conditional expression (9) can be appropriately shared by the two refracting surfaces, and the occurrence of aberrations can be suppressed here.

The imaging lens described in Item 16 satisfies the following conditional expression in the configuration described in Item 15.
0.30 <r7 / f <1.0 (11)
Conditional expression (11) is for appropriately setting the refractive power of the object side surface of the fourth lens. By satisfying conditional expression (11), the refractive power of the air lens defined by conditional expression (9) can be more appropriately shared by the two refracting surfaces, and the occurrence of aberrations can be suppressed here.

In the imaging lens according to Item 17, in the structure according to Items 1 to 16, the first lens is formed from a glass material, and the second lens, the third lens, and the fourth lens are formed from a plastic material. The following conditional expression is satisfied.
| F / f234 | <0.5 (12)
However,
f: Focal length of the entire lens system f234: Composite focal length of the second lens, the third lens, and the fourth lens formed from a plastic material All the lenses constituting the imaging lens are plastic lenses manufactured by injection molding. This configuration is advantageous for reducing the size and weight of the imaging lens and reducing the cost. However, since the plastic material has a large refractive index change at the time of temperature change, if all the lenses are made of plastic lenses, the image point position of the entire lens varies depending on the temperature.

  Therefore, the positive first lens is formed from a glass material that hardly changes the refractive index when the temperature changes, and the other second lens, third lens, and fourth lens are formed of a plastic material. While being frequently used, it is possible to compensate for image point position fluctuations at the time of temperature change in the entire lens system. By optimizing the refractive power distribution of the second, third, and fourth lenses, the contribution to the image point position fluctuation at the time of temperature change is canceled out, and the image point position fluctuation at the time of temperature change in the entire lens system. Can be kept small.

  In addition, when the first lens is a glass lens, it is not necessary to expose a plastic lens that is easily damaged, and a preferable configuration can be obtained.

Conditional expression (12) defines the combined focal length of the second lens, the third lens, and the fourth lens made of plastic. By reducing the combined refractive power (increasing the combined focal length) so as to satisfy the conditional expression, the image point position fluctuation at the time of temperature change can be suppressed small. The range of the following formula is desirable.
| F / f234 | <0.35 (12 ′)
Since the imaging device according to Item 18 includes the imaging lens according to any one of Items 1 to 17 and a solid-state imaging device, a small and high-performance imaging device can be obtained by using the imaging lens of the present invention. Obtainable.

  Hereinafter, although embodiments and examples of the present invention will be described in detail with reference to the drawings, the present invention is not limited to these embodiments and examples. In the present invention, the “plastic lens” includes a lens having a plastic material as a base material, molded from a material in which small-diameter particles are dispersed in the plastic material, and having a plastic volume ratio of more than half, This includes cases where the surface is coated for the purpose of preventing reflection or improving surface hardness.

  An imaging lens with a wide shooting angle of view is often desired for an imaging device mounted on a mobile phone or a small information terminal. For example, there is a usage in which a photographer extends an arm, has an imaging device or an information device equipped with the imaging device, and photographs the subject as a subject. The angle of view suitable for such shooting is approximately 60 ° or more. Further, in the case of having a requested digital zoom function that changes the apparent photographing range by enlarging and displaying a part of the photographed digital image, it is desirable that the photographing lens has as wide a photographing angle of view as possible. Therefore, in this specification, the term “wide-angle imaging lens” refers to a focal length of 38 mm or less, preferably about 35 mm in terms of the focal length of an imaging lens compatible with 35 mm film, and has an angle of view of approximately 60 mm. It shall mean that which has more than °.

  Furthermore, an imaging lens used in an imaging device including a solid-state imaging device is required to be image side telecentric in order to obtain good light receiving sensitivity over the entire screen. Image-side telecentric means that the principal ray enters the imaging surface of the solid-state imaging device at an angle parallel to the optical axis at each image height. In recent years, it has become possible to correct the image-side telecentric dissatisfaction amount by appropriately arranging a microlens array on the imaging surface of a solid-state imaging device. Specifically, by setting the pitch of the arrangement of the microlens array slightly smaller than the pixel pitch of each pixel on the imaging surface, the microlens array moves toward the periphery of the screen so that the microlens array moves toward the periphery of the screen. Since it is shifted to the side, the obliquely incident light beam can be efficiently guided to the light receiving portion of each pixel. At this time, in order to obtain good light receiving sensitivity and image quality over the entire screen, it is desirable that the chief ray incident angle on the imaging surface has a linearity as much as possible with respect to the image height. In this specification, the term “good telecentric characteristics” means that the incident angle of the principal ray at the outermost periphery of the imaging surface is about 25 ° or less.

  FIG. 1 is a sectional view in the optical axis direction of an image pickup apparatus including the image pickup lens of Example 1. In FIG. 1, the imaging lens includes an aperture stop S, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4 in order from the object side. The imaging lens and the image side of the imaging lens An image pickup apparatus is configured with an optical low-pass filter (for example, an infrared cut coat is applied to the object side surface) LPF, CMOS, or CCD such as a CCD, which is disposed in (1). An optical image that has passed through the imaging lens, the optical low-pass filter LPF, and the cover glass (parallel plate) CG of the solid-state imaging device IS and formed on the imaging surface I is photoelectrically converted by the solid-state imaging device IS, and further subjected to predetermined processing. Is converted into an image signal.

Here, an example suitable for the present embodiment will be described. The symbols used in the examples described below are as follows.
f: Focal length of the entire imaging lens system F: F number 2Y: Diagonal length 2ω of the rectangular effective pixel area of the imaging surface of the solid-state imaging device: Angle of view R (or r): Radius of curvature D (or d): Axis upper surface distance Nd (or nd): Refractive index of lens material with respect to d-line νd: Abbe number of lens material In each example, the aspherical shape is an orthogonal coordinate system with the vertex of the surface as the origin and the optical axis direction as the X axis. The vertex curvature is C, the conic constant is Κ, and the aspherical coefficients are A4, A6, A8, A10, and A12.

However,
Ai: i-th order aspheric coefficient C: curvature K: conic constant

(Example 1)
In the imaging lens suitable for the imaging apparatus shown in FIG. 1 (Example 1), the focal length (f), F number (F), and angle of view (2ω) are as follows.
f: 4.65 mm
F: 4.12
2ω: 63.2 °
Further, lens data of Example 1 is shown in Table 1. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰³ ) is represented using E (for example, 2.5E-03).

  FIGS. 2 (a) to 2 (d) are aberration diagrams of Example 1, and spherical aberration (FIG. 2 (a)), astigmatism (FIG. 2 (b)), and distortion, respectively. Aberration (FIG. 2 (c)) and meridional coma aberration (FIG. 2 (d)). In Example 1, the first lens, the third lens, and the fourth lens are formed of a polyolefin-based plastic material, and the saturated water absorption is 0.01% or less. The second lens is made of a polycarbonate plastic material and has a saturated water absorption of 0.4% or less.

(Example 2)
FIG. 3 is a sectional view in the optical axis direction of an image pickup apparatus including the image pickup lens of Example 2. In FIG. 3, the imaging lens includes, in order from the object side, an aperture stop S, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4. The imaging lens and the image side of the imaging lens. An image pickup apparatus is configured with an optical low-pass filter (for example, an infrared cut coat is applied to the object side surface) LPF, CMOS, or CCD such as a CCD, which is disposed in (1). An optical image that has passed through the imaging lens, the optical low-pass filter LPF, and the cover glass (parallel plate) CG of the solid-state imaging device IS and formed on the imaging surface I is photoelectrically converted by the solid-state imaging device IS, and further subjected to predetermined processing. Is converted into an image signal.

In the imaging lens suitable for the imaging apparatus shown in FIG. 3 (Example 2), the focal length (f), F number (F), and angle of view (2ω) are as follows.
f: 4.65 mm
F: 4.12
2ω: 63.2 °
Further, Table 2 shows lens data of Example 2. FIGS. 4 (a) to 4 (d) are aberration diagrams of Example 2, and spherical aberration (FIG. 4 (a)), astigmatism (FIG. 4 (b)), and distortion, respectively. Aberration (FIG. 4 (c)) and meridional coma aberration (FIG. 4 (d)).

  In Example 2, the first lens, the third lens, and the fourth lens are formed of a polyolefin-based plastic material, and the saturated water absorption is 0.01% or less. The second lens is made of a polycarbonate plastic material and has a saturated water absorption of 0.4% or less.

(Example 3)
FIG. 5 is a cross-sectional view in the optical axis direction of an imaging apparatus including the imaging lens of Example 3. In FIG. 5, the imaging lens includes an aperture stop S, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4 in order from the object side. The imaging lens and the image side of the imaging lens An image pickup apparatus is configured with an optical low-pass filter (for example, an infrared cut coat is applied to the object side surface) LPF, CMOS, or CCD such as a CCD, which is disposed in (1). An optical image that has passed through the imaging lens, the optical low-pass filter LPF, and the cover glass (parallel plate) CG of the solid-state imaging device IS and formed on the imaging surface I is photoelectrically converted by the solid-state imaging device IS, and further subjected to predetermined processing. Is converted into an image signal.

In the imaging lens suitable for the imaging apparatus shown in FIG. 5 (Example 3), the focal length (f), F number (F), and angle of view (2ω) are as follows.
f: 4.62 mm
F: 4.00
2ω: 62.7 °
Further, lens data of Example 3 is shown in Table 3. FIGS. 6 (a) to 6 (d) are aberration diagrams of Example 3, which are spherical aberration (FIG. 6 (a)), astigmatism (FIG. 6 (b)), and distortion, respectively. Fig. 6 shows aberrations (Fig. 6 (c)) and meridional coma aberration (Fig. 6 (d)).

  In Example 3, the first lens and the third lens are formed of a polyolefin-based plastic material, and the saturated water absorption is 0.01% or less. The second lens and the fourth lens are made of polycarbonate plastic material, and the saturated water absorption is 0.4% or less.

Example 4
FIG. 7 is a cross-sectional view in the optical axis direction of an imaging apparatus including the imaging lens of Example 4. In FIG. 7, the imaging lens includes, in order from the object side, an aperture stop S, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4, and the imaging lens and the image side of the imaging lens. An image pickup apparatus is configured with an optical low-pass filter (for example, an infrared cut coat is applied to the object side surface) LPF, CMOS, or CCD such as a CCD, which is disposed in (1). An optical image that has passed through the imaging lens, the optical low-pass filter LPF, and the cover glass (parallel plate) CG of the solid-state imaging device IS and formed on the imaging surface I is photoelectrically converted by the solid-state imaging device IS, and further subjected to predetermined processing. Is converted into an image signal.

In the imaging lens suitable for the imaging apparatus shown in FIG. 7 (Example 4), the focal length (f), F number (F), and angle of view (2ω) are as follows.
f: 4.65 mm
F: 2.88
2ω: 62.3 °
Furthermore, Table 4 shows lens data of Example 4. FIGS. 8 (a) to 8 (d) are aberration diagrams of Example 4, which are spherical aberration (FIG. 8 (a)), astigmatism (FIG. 8 (b)), and distortion, respectively. Aberration (FIG. 8 (c)) and meridional coma aberration (FIG. 8 (d)).

  In Example 4, the first lens and the third lens are made of a polyolefin-based plastic material, and the saturated water absorption is 0.01% or less. The second lens and the fourth lens are made of polycarbonate plastic material, and the saturated water absorption is 0.4% or less.

(Example 5)
FIG. 9 is a sectional view in the optical axis direction of an image pickup apparatus including the image pickup lens of Example 5. In FIG. 9, the imaging lens includes, in order from the object side, an aperture stop S, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4. The imaging lens and the image side of the imaging lens. An image pickup apparatus is configured by an infrared cut filter IRCF, a solid-state image pickup element IS such as a CMOS or CCD, which is disposed on the side surface of the object and has an infrared cut coat applied to the object side surface. An optical image that has passed through the imaging lens, the infrared cut filter IRCF, and the cover glass (parallel plate) CG of the solid-state imaging device IS and formed on the imaging surface I is photoelectrically converted by the solid-state imaging device IS, and further subjected to predetermined processing. By being applied, it is converted into an image signal.

In the imaging lens suitable for the imaging apparatus shown in FIG. 9 (Example 5), the focal length (f), F number (F), and angle of view (2ω) are as follows.
f: 4.62 mm
F: 4.00
2ω: 63.3 °
Further, Table 5 shows lens data of Example 5. FIGS. 10 (a) to 10 (d) are aberration diagrams of Example 5, which are spherical aberration (FIG. 10 (a)), astigmatism (FIG. 10 (b)), and distortion, respectively. Aberration (FIG. 10 (c)) and meridional coma aberration (FIG. 10 (d)).

  In Example 5, the curvature radii of the image side surface of the second lens and the object side surface of the third lens are equal, and they are adjacent to each other or bonded without interposing an air space therebetween. The first lens and the third lens are made of a polyolefin plastic material, and the saturated water absorption is 0.01% or less. The second lens and the fourth lens are made of polycarbonate plastic material, and the saturated water absorption is 0.4% or less.

(Example 6)
FIG. 11 is a cross-sectional view in the optical axis direction of an image pickup apparatus including the image pickup lens of Example 6. In FIG. 11, the imaging lens includes an aperture stop S, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4 in order from the object side. The imaging lens and the image side of the imaging lens The image pickup apparatus is configured by an optical low-pass filter (for example, an infrared cut coat is provided on the side surface of the object) LPF, a CMOS, or a CCD such as a CCD, which is disposed in (1). The optical image that has passed through the imaging lens, the optical low-pass filter LPF, and the cover glass (parallel plate) CG of the solid-state imaging device IS and formed on the imaging surface I is photoelectrically converted by the solid-state imaging device IS, and further subjected to predetermined processing. Is converted into an image signal.

In the imaging lens suitable for the imaging apparatus shown in FIG. 11 (Example 6), the focal length (f), F number (F), and angle of view (2ω) are as follows.
f: 4.65 mm
F: 4.12
2ω: 62.7 °
Table 6 shows lens data of Example 6. FIGS. 12 (a) to 12 (d) are aberration diagrams of Example 6, which are spherical aberration (FIG. 12 (a)), astigmatism (FIG. 12 (b)), and distortion, respectively. Fig. 12 shows aberrations (Fig. 12 (c)) and meridional coma aberration (Fig. 12 (d)).

  In Example 6, the first lens, the third lens, and the fourth lens are formed of a polyolefin-based plastic material, and the saturated water absorption is 0.01% or less. The second lens is made of a polycarbonate plastic material and has a saturated water absorption of 0.4% or less.

(Example 7)
FIG. 13 is a sectional view in the optical axis direction of an imaging apparatus including the imaging lens of Example 7. In FIG. 13, the imaging lens includes, in order from the object side, a first lens L1, an aperture stop S, a second lens L2, a third lens L3, and a fourth lens L4, and the imaging lens and the image side of the imaging lens. The image pickup apparatus is composed of an infrared cut filter IRCF having an infrared cut coat on the object side surface, a cover glass (parallel plate) CG of a solid-state image sensor IS, a solid-state image sensor IS such as a CMOS or a CCD. . An optical image that has passed through the imaging lens, the infrared cut filter IRCF, and the cover glass (parallel plate) CG of the solid-state imaging device IS and formed on the imaging surface I is photoelectrically converted by the solid-state imaging device IS, and further subjected to predetermined processing. By being applied, it is converted into an image signal.

In the imaging lens suitable for the imaging apparatus shown in FIG. 13 (Example 7), the focal length (f), F number (F), and angle of view (2ω) are as follows.
f: 5.50 mm
F: 2.88
2ω: 64.0 °
Table 7 shows lens data of Example 7. FIGS. 14 (a) to 14 (d) are aberration diagrams of Example 7. Spherical aberration (FIG. 14 (a)), astigmatism (FIG. 14 (b)), and distortion are shown respectively. Aberration (FIG. 14 (c)) and meridional coma aberration (FIG. 14 (d)).

  In Example 7, the first lens, the third lens, and the fourth lens are formed of a polyolefin-based plastic material, and the saturated water absorption is 0.01% or less. The second lens is made of a polycarbonate plastic material and has a saturated water absorption of 0.4% or less.

(Example 8)
FIG. 15 is a sectional view in the optical axis direction of an image pickup apparatus including the image pickup lens of Example 8. In FIG. 15, the imaging lens includes, in order from the object side, a first lens L1, an aperture stop S, a second lens L2, a third lens L3, and a fourth lens L4, and the imaging lens and the image side of the imaging lens. The image pickup apparatus is composed of an infrared cut filter IRCF having an infrared cut coat on the object side surface, a cover glass (parallel plate) CG of a solid-state image sensor IS, a solid-state image sensor IS such as a CMOS or a CCD. . An optical image that has passed through the imaging lens, the infrared cut filter IRCF, and the cover glass (parallel plate) CG of the solid-state imaging device IS and formed on the imaging surface I is photoelectrically converted by the solid-state imaging device IS, and further subjected to predetermined processing. By being applied, it is converted into an image signal.

In the imaging lens suitable for the imaging apparatus shown in FIG. 15 (Example 8), the focal length (f), F number (F), and angle of view (2ω) are as follows.
f: 5.53 mm
F: 2.88
2ω: 63.5 °
Table 8 shows lens data of Example 8. FIGS. 16 (a) to 16 (d) are aberration diagrams of Example 8, which are spherical aberration (FIG. 16 (a)), astigmatism (FIG. 16 (b)), and distortion, respectively. Aberration (FIG. 16 (c)) and meridional coma aberration (FIG. 16 (d)). In Example 8, the first lens is formed of a glass mold lens, and the second lens is formed of a polycarbonate plastic material, and the saturated water absorption is 0.4% or less. The third lens and the fourth lens are made of a polyolefin-based plastic material and have a saturated water absorption rate of 0.01% or less.

Example 9
FIG. 18 is a cross-sectional view in the optical axis direction of an imaging apparatus including the imaging lens of Example 9. In FIG. 18, the imaging lens includes, in order from the object side, a first lens L1, an aperture stop S, a second lens L2, a third lens L3, and a fourth lens L4, and the imaging lens and the image side of the imaging lens. The image pickup apparatus is configured by the arranged infrared cut filter IRCF having an infrared cut coat on the object side surface, and a solid-state image pickup element IS such as a CMOS or a CCD. An optical image that passes through the imaging lens and the infrared cut filter IRCF and is imaged on the imaging surface I is photoelectrically converted by the solid-state imaging device IS, and further subjected to predetermined processing so as to be converted into an image signal. It has become.

  In the imaging lens suitable for the imaging apparatus shown in FIG. 18 (Example 9), the values of the focal length (f), F number (F), and angle of view (2ω) are as follows.

f: 4.66 mm
F: 3.60
2ω: 63.3 °
Table 9 shows lens data of Example 9. FIGS. 19 (a) to 19 (d) are aberration diagrams of Example 9, which are spherical aberration (FIG. 19 (a)), astigmatism (FIG. 19 (b)), and distortion, respectively. Aberration (FIG. 19 (c)) and meridional coma aberration (FIG. 19 (d)). In Example 9, the first lens is a glass mold lens, the second lens, and the fourth lens are formed of a polycarbonate plastic material, and the saturated water absorption is 0.4% or less. The third lens is made of a polyolefin plastic material and has a saturated water absorption of 0.01% or less.

  Table 10 summarizes the values of conditional expressions (1) to (12) for each example.

  If all the lenses constituting the imaging lens are made of plastic lenses manufactured by injection molding, mass production is possible, and it is easy to add an aspheric surface, so that the lens performance can be improved. On the other hand, there is a problem that the image point position fluctuates due to a change in the refractive index of the plastic material due to a change in the outside air temperature. In recent years, however, an imaging apparatus equipped with an autofocus (AF) mechanism has also been used. In such an imaging apparatus, the fluctuation of the image point position is not a problem. Strictly speaking, in an imaging apparatus having a function such as a mode for fixing the focal point at a focal distance or infinity even if the AF mechanism is mounted, another means for correcting the fluctuation of the image point position is required. . In such a case, a separate temperature sensor may be mounted and correction such as fine adjustment of the distance between the imaging lens and the imaging surface of the solid-state imaging device may be performed based on temperature information from the temperature sensor.

  In an imaging apparatus not equipped with an AF mechanism, fluctuations in image point position due to changes in outside air temperature tend to be a problem. In such a case, a positive lens having a strong refractive power (for example, the first lens in the present invention) is a glass mold lens formed of a glass material, and the total refractive power of the remaining plastic lenses is small. By suppressing the value to this value, it is possible to reduce the fluctuation of the image point position when the temperature changes.

Recently, it has been found that inorganic fine particles can be mixed in a plastic material to suppress the temperature change of the refractive index of the plastic material to a small value. More specifically, mixing fine particles with a transparent plastic material generally causes light scattering and lowers the transmittance, so it was difficult to use as an optical material. By making it smaller than the wavelength, it is possible to substantially prevent scattering. The refractive index of the plastic material decreases with increasing temperature, but the refractive index of inorganic particles increases with increasing temperature. Therefore, it is possible to make almost no change in the refractive index by using these temperature dependencies so as to cancel each other. Specifically, by dispersing inorganic particles having a maximum length of 20 nanometers or less in a plastic material as a base material, a plastic material with extremely low temperature dependency of the refractive index is obtained. For example, by dispersing fine particles of niobium oxide (Nb ₂ O ₅ ) in acrylic, the refractive index change due to temperature change can be reduced. By using such a plastic material in which inorganic particles are dispersed, it is possible to suppress the fluctuation of the image point position when the temperature of the entire imaging lens system changes.

  According to the present invention, it is possible to provide a four-group four-lens imaging lens and an imaging device using the same, which are small in size, have various aberrations corrected well, and have good image-side telecentric characteristics.

1 is a cross-sectional view in the optical axis direction of an imaging device including an imaging lens of Example 1. FIG. FIG. 4 is aberration diagrams of Example 1, and shows spherical aberration (FIG. 2 (a)), astigmatism (FIG. 2 (b)), distortion aberration (FIG. 2 (c)), and meridional coma aberration, respectively. (FIG. 2 (d)). 6 is a cross-sectional view in the optical axis direction of an imaging apparatus including an imaging lens of Example 2. FIG. FIG. 4 is aberration diagrams of Example 2, which are spherical aberration (FIG. 4 (a)), astigmatism (FIG. 4 (b)), distortion aberration (FIG. 4 (c)), and meridional coma aberration, respectively. (FIG. 4 (d)). 7 is a cross-sectional view in the optical axis direction of an imaging apparatus including an imaging lens of Example 3. FIG. FIG. 6 is aberration diagrams of Example 3, which are spherical aberration (FIG. 6 (a)), astigmatism (FIG. 6 (b)), distortion aberration (FIG. 6 (c)), and meridional coma aberration, respectively. (FIG. 6 (d)). 6 is a cross-sectional view in the optical axis direction of an imaging apparatus including an imaging lens of Example 4. FIG. FIG. 6 is aberration diagrams of Example 4, which are spherical aberration (FIG. 8 (a)), astigmatism (FIG. 8 (b)), distortion aberration (FIG. 8 (c)), and meridional coma aberration, respectively. (FIG. 8 (d)). 6 is a cross-sectional view in the optical axis direction of an imaging apparatus including an imaging lens of Example 5. FIG. FIG. 10 is aberration diagrams of Example 5, which are spherical aberration (FIG. 10 (a)), astigmatism (FIG. 10 (b)), distortion aberration (FIG. 10 (c)), and meridional coma aberration, respectively. (FIG. 10 (d)). 10 is a cross-sectional view in the optical axis direction of an imaging apparatus including an imaging lens of Example 6. FIG. FIG. 10 is aberration diagrams of Example 6. Spherical aberration (FIG. 12 (a)), astigmatism (FIG. 12 (b)), distortion (FIG. 12 (c)), and meridional coma aberration, respectively. (FIG. 12 (d)). FIG. 9 is a cross-sectional view in the optical axis direction of an imaging apparatus including an imaging lens of Example 7. FIG. 9 is aberration diagrams of Example 7, which are spherical aberration (FIG. 14 (a)), astigmatism (FIG. 14 (b)), distortion (FIG. 14 (c)), and meridional coma aberration, respectively. (FIG. 14 (d)). 10 is a cross-sectional view in the optical axis direction of an imaging apparatus including an imaging lens of Example 8. FIG. FIG. 10 is aberration diagrams of Example 8, which are spherical aberration (FIG. 16 (a)), astigmatism (FIG. 16 (b)), distortion (FIG. 16 (c)), and meridional coma aberration, respectively. (FIG. 16 (d)). It is sectional drawing of the example which shows the 1st lens attached to the light shielding member of an imaging device with a light shielding member. 10 is a cross-sectional view in the optical axis direction of an imaging apparatus including an imaging lens of Example 9. FIG. 10 is aberration diagrams of Example 9, spherical aberration (FIG. 19 (a)), astigmatism (FIG. 19 (b)), distortion aberration (FIG. 19 (c)), and meridional coma aberration, respectively. (FIG. 19 (d)).

Claims (18)

In order from the object side, a first lens having positive refractive power (hereinafter positive lens), a second lens having negative refractive power (hereinafter negative lens), a third lens being a positive lens, and at least one surface is aspherical. An imaging lens comprising a fourth lens having a shape and satisfying the following conditional expression:
−3.0 <(r3 + r4) / (r3−r4) <− 0.7 (1)
ν1-ν2> 15.0 (2)
ν3-ν2> 15.0 (3)
r3: radius of curvature of object side surface of second lens r4: radius of curvature of image side surface of second lens ν1: Abbe number of first lens ν2: Abbe number of second lens ν3: Abbe number of third lens The imaging lens according to claim 1, wherein the imaging lens has an aperture stop closest to the object side. The imaging lens according to claim 2, wherein the following conditional expression is satisfied.
-1.5 <(r3 + r4) / (r3-r4) <-0.7 (4)
r3: radius of curvature of object side surface of second lens r4: radius of curvature of image side surface of second lens The imaging lens according to claim 2, wherein the following conditional expression is satisfied.
-1.5 <(r3 + r4) / (r3-r4) <-1.0 (5)
r3: radius of curvature of object side surface of second lens r4: radius of curvature of image side surface of second lens The imaging lens according to claim 2, wherein the following conditional expression is satisfied.
0.1 <(r1 + r2) / (r1-r2) <1.0 (6)
r1: radius of curvature of the object side surface of the first lens r2: radius of curvature of the image side surface of the first lens The imaging lens according to claim 2, wherein the fourth lens is a positive lens. The imaging lens according to claim 2, wherein the fourth lens is a negative lens. The imaging lens according to claim 1, wherein the imaging lens has an aperture stop between the first lens and the second lens. The imaging lens according to claim 8, wherein the first lens has a shape with a convex surface facing the object side. The imaging lens according to claim 8, wherein the following conditional expression is satisfied.
-1.5 <f2 / f <-0.7 (7)
f2: Focal length of the second lens f: Focal length of the entire imaging lens system 9. The range according to claim 8, wherein the first lens and the second lens in the imaging lens each have a meniscus shape with a concave surface facing the aperture stop side with the aperture stop interposed therebetween. Imaging lens. The imaging lens according to claim 8, wherein the following conditional expression is satisfied.
-2.5 <(r3 + r4) / (r3-r4) <-1.2 (8) The imaging lens according to claim 8, wherein the fourth lens is a negative lens. The imaging lens according to claim 1, wherein an air lens formed by an image side surface of the third lens and an object side surface of the fourth lens in the imaging lens has a biconcave shape. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
0.30 <fa / f <0.60 (9)
0.30 <r7 / f <2.0 (10)
f: Focal length of the entire imaging lens system fa: Focal length of an air lens formed by the image side surface of the third lens and the object side surface of the fourth lens, which is calculated by the following formula: fa = R6 · R7 /{R7.(1-N3)+R6.(N4-1)-D6.(1-N3).(N4-1)}
However,
N3: Refractive index with respect to d-line of third lens N4: Refractive index with respect to d-line of fourth lens R6: Radius of curvature of image side surface of third lens R7: Radius of curvature of object side surface of fourth lens D6: With third lens Air spacing on the axis of the fourth lens r7: radius of curvature of the object side surface of the fourth lens The imaging lens according to claim 15, wherein the following conditional expression is satisfied.
0.30 <r7 / f <1.0 (11) The first lens is formed of a glass material;
2. The imaging lens according to claim 1, wherein the second lens, the third lens, and the fourth lens are made of a plastic material and satisfy the following conditional expression.
| F / f234 | <0.5 (12)
However,
f: focal length of the entire lens system f234: combined focal length of the second lens, the third lens, and the fourth lens made of a plastic material An imaging apparatus comprising the imaging lens according to claim 1 and a solid-state imaging device.

Images